Two-cycle engines are used to power watercraft, including smaller watercraft known as "personal" watercraft. These engines have the advantage that they are fairly powerful, and relatively lightweight and compact.
One particular disadvantage to the two-cycle engine is its emission content. Two-cycle engines exhaust large quantities of carbon monoxide (CO) and various hydrocarbons. When measures are taken to reduce the emission content of the two-cycle engine, other generally undesirable consequences result, such as an increase in the weight of the engine, a reduction of its power output or the like.
Four-cycle engines are commonly used as a power plant in other applications, such as automobiles. These engines have the advantage that their emission content is desirably lower and the engines have a high power output.
On the other hand, heat build-up is a concern when utilizing four-cycle engines in enclosed spaces such as an engine compartment of a watercraft. If inadequately cooled, high temperatures in the combustion chambers may decrease engine performance. In addition, heat generated by the engine may be transmitted to surrounding engine components within the engine compartment enclosed within the hull, causing them to be damaged. If the engine becomes too hot, it may also be hard to restart.
An arrangement for adequately cooling a four-cycle engine for use in a personal watercraft application is desired.